vos_catalog.py: fix use of format() for compat with python 2.6
another {} format() problem in test_cosmology
status -> "param_jac" in NonLinearLSQFitter
Add param_cov to fit_info
Added  documentation for `fit_info`
Added test for param_cov
fix error in errorfunc usage revealed by tests
change param_jac to cov_x, because it's not really a jacobian
Added support for trailing Z in UTC time
Fixed error message, added tests for trailing Z
Added exception test for non-utc
Don't fail -P if docs missing
Update docguide.rst

typo fix
Restructure front documentation page to emphasize contributions rather than development
Example of reworked documentation aimed at beginners
Clarify language in several places
Change line breaks to keep length under 80 characters
Fix typographical errors
Add caveats about cases when setup.py develop will fail
Clarify warning about need to reactive development astropy

New wording suggested by @mdboom